This invention relates in general to motorcycles and more particularly to motorcycle frames.
Motorcycles have long been a popular means of transportation, partly because their small size and construction makes them a very maneuverable and efficient motor vehicle. Although motorcycles have been constructed of various shapes, sizes and designs, they all have one element in common, namely some type of structural frame which is supported by the front and back wheels and which in turn, supports the rider and power source. The most common type of motorcyle frame at the present time is one which carries the engine generally centrally between the front and rear wheels and which provides support means for seating the passenger above the engine.
Despite the popularity of such motorcycle frames, there are several heretofore unresolved problems characteristic of this type of motorcycle frame construction. Due to the fact that such frames are generally almost as tall as they are long, excluding the front wheel fork, they tend to take on a somewhat boxy shape with ample vertical reinforcing members to produce a rigid structure. This is generally the intended result with the idea that the motorcycle suspension means, rather than the frame, should provide any desired comfort by absorbing the vertical forces induced by travel over rough surfaces.
Accordingly, it is one object of the present invention to construct a motorcycle frame which itself has inherent flexibility for increased rider comfort.
Such ample frame reinforcement also tend to complicate the design of the motorcycle since the additional structural members must be designed around in order to position the various other parts and accessories of the motorcycle. It is another object of the present invention therefore to provide a frame having a simplified uncomplicated construction which permits considerable variation in the design of the motorcycle to be built thereon. Besides the rigidity of such frames, an almost universal passenger discomfort is the positional relationship of the rider directly above the motorcycle engine. The rider must be ever cautious that his lower extremities are not scorched by accidental contact with the very hot exposed surfaces of the motorcycle engine such as the exhaust pipes, cooling fins or engine block itself. Even regardless of proper safeguards to prevent physical contact with the motorcycle engine, a rider is nevertheless subject to the constant heat and noise exposure to the engine over which he is seated. It is therefore a further object of the present invention to provide a motorcycle frame adopted to situate the rider and passenger in front of the motorcycle engine in order to prevent physical contact and exposure to the heat and noise incident to a running motorcycle engine.
The performance of the motorcycle is also somewhat stifled by the conventional frame design described above. A rider, seated above the motorcycle engine, with his legs spread to straddle the engine, presents additional wind-resisting surfaces which require valuable energy of the motorcycle engine to be consumed resisting the resultant increased passenger wind resistance. Furthermore, the rider or rider and passenger, who are situated on a padded saddle mounted above the engine, tend to elevate the center of gravity of the motorcycle substantially above the axle centerline. The higher the center of gravity is above the axle centerline, the less stable the vehicle becomes. Another object of the present invention is thus to provide a motorcycle frame on which the rider and passenger may be situated close to the axle centerline of the motorcycle and longitudinally in line with the motorcycle engine, thereby to substantially reduce wind resistance and to minimize the rider's effect of elevating the motorcycle's center of gravity. Referring now to the longitudinal dimensions of the conventional frame, it will be observed that the torque exerted by the rear wheel during acceleration, which would tend to raise the bike up onto its rear wheel alone as in the "wheely" position, must be resisted almost entirely by the weight of both the passengers and engine acting through one and the same length of leverage arm, since they are positioned one above the other. It is an object of the present invention to permit increased acceleration of the motorcycle by positioning the engine and rider so as to have a greater torque resistant effect.
Specifically, in accordance with the present invention, flexibility is imparted to the motorcycle frame of the present invention by its elongated construction including a plurality of frame tubes running through substantially the entire length of the frame and so constructed as to provide support portions for a rider and passenger in front of the intended engine compartment, as opposed to the conventional position above it. The frame consists of a pair of frame sections, each including at least one frame tube, with the frame sections situated generally symmetrically about a longitudinal vertical plane located between the frame sections. The tubes of each section are juxtaposed one to another substantially in a parallel run relation at a medial portion of the frame to define the bottom of a passenger compartment, with the parallel runs being laterally opposite one another and within the same horizontal plane. Steering post support portions of the tubes are rigidly connected to a steering post and extend rearwardly therefrom flaring laterally outwardly and downwardly into the parallel runs. Rearwardly of the parallel runs, tubes of each pair of frame sections incline vertically upwardly and extend rearwardly to define an engine compartment which is thus located behind the passenger compartment and mostly above the horizontal plane.
With the passengers thus positioned in front of rather than above the engine compartment, the dangerous possibility of passenger contact with the engine while running is practically eliminated and the passengers are removed from the noise and heat of the engine. In this connection, since the passengers are seated on approximately the same horizontal plane which underlies the greater portion of the engine compartment, the weight of the passengers has little or no effect of elevating the center of gravity of the motorcycle vehicle, which results in greater ride stability. A further characteristic of such an arrangement is, of course, that wind resistance is minimized since the rider is positioned substantially within the wind resisting area of the motorcycle itself. The simplicity of the structure of the present invention results from the comstruction of the elongated frame tubes which may be the only longitudinally directed members of the frame. Lateral reinforcement may be provided simply by one or more frame cross members laterally spanning the motorcycle frame rearwardly of the steering post support and fastened to at least one tube of each frame section. In order to permit increased acceleration of the motorcycle, the motorcycle frame of the present invention is so constructed that the weight of the passengers, positioned in front of the motorcycle engine, thus acts through a longer leverage arm than the engine. The forces which resist the moment created about the rear wheel upon acceleration are thus increased and the probability of raising the front end of the cycle while accelerating is substantially reduced.